Abstract:
In Part II a large-scale sound source in a time-developing planar free mixing layer is studied using an acoustic analogy approach. It is shown that only the non-compact character of the source resembles well the character of the corresponding source in a spatially developing flow. A model based on a continuous assembly of wave packets is derived and applied to direct numerical simulation results of two supersonic time-developing mixing layers undergoing transition to turbulence. The analysis predicts two distinctive dominant Mach wave sources in agreement with the direct analysis of Part~I. The first dominates during the stage of the Λ-vortex structure and the second just prior to the final breakdown to a fine-scale structure. The convective velocity of the second Mach wave source is higher than the first and thus its Mach angle of radiation is higher. The second source has a reduced strength at the higher free-stream Mach number. Directivity and frequency spectra compare well with the results of Part I, demonstrating that the assumptions inherent in the analogy are quite reasonable.
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Received 5 August 1997 and accepted 6 April 1998
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Avital, E., Sandham, N. & Luo, K. Mach Wave Radiation by Mixing Layers. Part II: Analysis of the Source Field . Theoret. Comput. Fluid Dynamics 12, 91–108 (1998). https://doi.org/10.1007/s001620050101
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DOI: https://doi.org/10.1007/s001620050101